The importance of equipment maintenance in ensuring product quality and plant safety has long been recognized. More recently, industry has begun to understand the impact of maintenance practice on broader elements of manufacturing productivity, such as factory output and product cycle time, as well as on product yield. Rising maintenance costs as a percentage of total operating costs, as well as market pressure to produce competitively priced products, have generated increased awareness and interest in equipment maintenance in industries as diverse as semiconductors and electric utilities. In such equipment-intensive industries, even small improvements in equipment utilization can result in an immediate competitive advantage. Maintenance technology has improved dramatically in the last decade with the development of sophisticated sensors that allow for on-line monitoring of critical process and equipment parameters. At the same time, new operational analysis tools that enable better decision making at the planning and operational stages have become available.